Survivors described a night of screaming and chaos after the derailment and said it took rescuers more than three hours to reach the scene. The blue passenger train and the red cargo train were knotted together in mangled metal along a rural stretch of track near the small town of Sardiha, about 90 miles west of Calcutta in West Bengal state.

Officials disagreed on the cause of the derailment, with some saying it was caused by an explosion but others blaming sabotaged rail lines. Home Minister Palaniappan Chidambaram said in a statement that a section of the railway tracks had been cut, but “whether explosives were used is not yet clear.”

Bhupinder Singh, the top police official in West Bengal, said posters from the People’s Committee Against Police Atrocities, a group local officials believe is closely tied to the Maoists, had been found at the scene taking responsibility for the attack.

However, a spokesman for the group, Asit Mahato, denied any role, the Press Trust of India news agency reported.

“We were in no way involved. This is not our act,” PTI quoted him as saying by phone.

The area is an isolated, rural stronghold of India’s Maoist rebels, known as Naxalites, who have stepped up attacks in recent months and had called for a four-day general strike starting today.